Though Portal doesn't allow the player to carry any weapons per se, that doesn't mean no hostiles will appear to antagonize the test subject during her adventure. Certain levels feature stationary turrets that open fire once the player comes into view. Each turret is equipped with a roaming eye--visible to the player by way of the eye's red laser trail--that searches for trespassers before entering an idle state after several seconds. Without any weapons, how can the test subject possibly stand up to her robotic assailants? With the portal gun, of course.

The most entertaining way to disable a turret is to use another turret. Set one portal beneath a turret, place the second portal above another sentry, and watch as the first vanishes into the floor, falls through the ceiling, and collides with its comrade. It's a thing of beauty to behold, and really forces players to consider new ways to dispatch their enemies. The player might not be able to directly fight, but fighting back is most certainly an option.

Certain puzzles also make use of turrets. As players progress, they will undoubtedly notice that objects can pass from portal to another. Upon occasion, players can have objects separated by several rooms traverse areas within seconds, and along the way, players will happen by a few instances where firing projectiles through portals and into certain objects is the only way to progress.

Along the same lines, doors are rarely used in Portal; after all, the player has the ability to create his own, so why use a pre-made, old-fashioned object with a handle? Doors need to be opened sometimes, but usually, it pays to consider the possibilities of going around them, not through them.

Just when players think they finally have their minds wrapped around Portal's discombobulating gameplay mechanics, Advanced and trial variations of each course are unlocked upon completing the main game. Challenges such as completing floors in the least amount of time and, even harder, using a set number of portals awaits those who crave more complex spatial challenges.

Many Half-Life fanatics are no doubt wondering how, if at all, Portal ties into Gordon Freeman's storyline. Do the two characters know one another? Is there a connection between the events taking place at Aperture and the events devastating City 17, as well as countless other cities? Even more curious, with so many similarities between Aperture Labs and the Black Mesa science facility, might the two shady companies be connected in some capacity?

And the biggest question: Will the portal gun make an appearance in Half-Life 2: Episode Three? Imagine the combat and puzzle possibilities if players were to wield only the Zero-Point Energy Field Manipulator and the portal device? Staggering, and oh-so-fun to imagine.

Gamers who have been imagining the unique gameplay possibilities offered through Portal need not imagine much longer, as The Orange Box is less than a week away from arriving in stores. Packaged with Half-Life 2, its two episodic installments, and Team Fortress 2, Portal is part of a winning team guaranteed to make an impact this holiday season.